From Lakota America: A New History of Indigenous Power, by Pekka Hämäläinen (The Lamar Series in Western History; Yale U. Press, 2019), Kindle pp. 192-193:
In the winter of 1830 Lakotas killed some twenty Crows at Matȟó Pahá (Bear Butte) about twenty miles north of the fabled Racetrack. Crows had attempted to surprise a Lakota camp in an unusually snowy winter, but Lakota herders had detected them. Numerous winter counts recorded the battle, underscoring its importance: it marked the beginning of a war that would last, with short respites, for nearly half a century between Lakotas and Crows—the longest known war in the history of North America.
That the battle took place at Bear Butte was significant. Lakotas had banished Crows from the Black Hills in the 1820s, but the violence persisted, turning a vast arc stretching from the hills toward the North Platte, the Big Horn Mountains, and the Yellowstone into a battleground. At stake were spiritually significant places like Matȟó Pahá and Matȟó Thípila Pahá (Devil’s Tower) where Crows, Lakotas, and Cheyennes gathered to hold ceremonies and seek visions. At stake were also robes, protein, carbohydrates, and timber. The contested terrain, an alluring mosaic of steppes and mountains punctuated by a series of lush and well-forested river valleys, was rich in bison and wild plants and made for some of the best horse pastures in the Great Plains. The fighting became unyielding, bringing violence to the doorstep of the Lakota villages. An 1837 Oglala winter count reported one such incident: “Black-face, who painted half his face black from the nose down, camped away from the circle and was killed by the Crow, he and his whole family.”
The Crow war presented a singular challenge for Lakotas: it was their first full-blown conflict with other horse nomads. Crows were formidable warriors who had acquired horses long before Lakotas, possessed more animals per capita, and were generally known as superior equestrian fighters. They were also well integrated in the fur trade. They visited Fort Union near the Missouri-Yellowstone confluence every year and also rendezvoused with Rocky Mountain trapper-traders who considered the quality of Crow beaver pelts second to none. From both outlets guns, powder, and lead flowed into the Crow country. The experienced fur trader Denig considered the Crows “cunning, active, and very intelligent in everything appertaining to the chase, war, or their own individual bargaining.” Powerful and confident, they looked the part to Denig’s nineteenth-century sensibility. “The warrior class is perhaps the handsomest body of Indians in North America. They are all tall, straight, well formed, with bold, fierce eyes, and as usual good teeth. These also dress elegantly and expensively.”
The Crow-Lakota conflict was an uncompromising tug-of-war over the control of the borderlands that separated the Black Hills from the Crow country to the west. This meant that Crows were fighting in terrain they knew intimately and that Lakotas were entering foreign lands to face an enemy that matched or surpassed their firepower and horsemanship. But Lakotas had a number of advantages that compensated for their weaknesses. Their population dwarfed the five-thousand-strong Crows, and their clustering in Pahá Sápa allowed them to coordinate military action at an unprecedented scale. At the moment the Black Hills became home, they also became a front line.